Shorthand property of background

Question

When using the shorthand property for background in css is it necessary to be strict to the order of the values?
In w3schools.com they say u have but i tried my own in a different order and it worked .
I am confused

Answer 1

You have to, since some of the properties have same words.

Answer 2

but why it worked with me

Answer 3

Background size must be after background position with char /